Abrasive flap brushes are surface conditioning tools that include a central core and a plurality of radially extending strips, or flaps, of abrasive material. The abrasive flaps are each adhered to the core at one end of the flap, such that an opposed end of each flap is presented for contact with a workpiece surface when the core is rotated. Flap brushes of this construction are useful in the surface preparation and conditioning of metals, wood, plastics, and other materials to prepare the surface for painting, plating, or other subsequent processes. Flap brushes are also useful for imparting a desired finish to a surface of a workpiece.
FIG. 1 is a perspective view of a conventional flap brush 10, including a cylindrical central core 12, a layer of adhesive 16 coated on the outer peripheral surface 14 of the core, and a plurality of radially extending abrasive flaps 18. The cylindrical core 12 is typically a paper and phenolic resin composite or a polyester and glass fiber composite. The adhesive 16 may be, for example, an epoxy, and is coated over the outer surface 14 of the core to adhere the abrasive flaps 18 to the core 12. The abrasive flaps 18 may be nonwoven materials comprising staple fibers, abrasive particles, and a curable binder for bonding the particles to the nonwoven fibers. Flaps 18 are adhered at core end 20 to core 12 by the adhesive layer 16. The flaps 18 extend radially outwardly from the core 12, and are typically tightly packed to minimize relative movement between adjacent abrasive flaps. For example, in an abrasive flap brush having a 15.2 cm (6 in) outer diameter and including one hundred and twenty eight nonwoven abrasive flaps, the flaps 18 can be compressed at the core end 20 to approximately 10% of their uncompressed thickness and at their outer end 22 to about 30% of their uncompressed thickness. In this arrangement, the outer ends 22 of each of the abrasive flaps together form a flap brush outer peripheral surface 24, which may be rotatively applied to a workpiece surface. An example of a flap brush 10 of the foregoing general construction is available from the Minnesota Mining and Manufacturing Company of St. Paul, Minn. under the designation Scotch-Brite.TM. Flap Brush and is shown in FIG. 1.
The flap brush 10 shown in FIG. 1 is typically constructed by coating adhesive 16 over the outer surface 14 of a long central core 12 which can be 1.42 meters (56 in) long, for example, using art adhesive coater 50 as seen in FIG. 2. Coater 50 includes a cylindrical bore 52 having an inner diameter at wall 54 that is somewhat larger than the outer diameter of the core resulting in a gap 56 between the outer surface 14 and wall 54. Enough adhesive 16 to coat the core is held in funnel portion 58 of coater 50. Valve 60 can be moved in the opposing directions indicated by arrow A, and initially rests against the inner wall of the funnel 58 where it joins the bore 52. This prevents the adhesive from flowing into the space 56 between the bore wall 54 and the core 12. When valve 60 is lifted away from the wall of the funnel portion 58 to its open position, adhesive flows into space 56 between core 12 and bore wall 54, and bonds to outer surface 14 of core 12. Any suitable known means for maintaining the valve 60 in its open position may be used such as a pin and groove interlock with a frame member (not shown). The first end 13 of core 12 is moved in direction B through the bore such that the adhesive is progressively applied to outer surface 14 along the full length of the core to second end 15 in a relatively uniform manner. The longitudinal axis 11 of core 12 must be maintained sufficiently concentric relative to the longitudinal axis 53 of the bore of the coater, and the shape of the core must not be excessively out-of-round. In this manner, a sufficiently uniform coating of adhesive 16 will be applied around the entire outer surface 14 of the core 12 to adequately adhere substantially all of the core ends 20 of the abrasive flaps 18 to the core. In an attempt to maintain the core 12 concentric with the bore 52 of the coater, the inner wall 62 of valve 60 may be sized to be as close as possible in diameter to the outer surface 14 of the core, allowing for manufacturing tolerances, while still allowing the core 12 to pass through the valve 60. The valve 60 is then held by a suitable frame member (not shown) to be concentric to the bore 54, to keep the core 12 concentric with the bore 54.
After the adhesive has been applied to the core 12 by the coater, a plurality of abrasive flaps 18 which can be 1.32 meters (52 in) long, 5.08 cm (2 in) wide, and 1.27 cm (0.5 in) thick, for example, are compressed inwardly toward the core 12 to contact the adhesive 16. The long abrasive flaps 18 may be placed in contact with the adhesive 16 on the core 12 one after another, or more typically may be collectively compressed against the adhesive 16 until the adhesive cures. When the adhesive has cured sufficiently to retain the abrasive flaps 18, the long assembled abrasive flap brush may be cut transverse to the length of the core to provide a plurality of abrasive flap brushes 10 of any suitable width. Each flap brush may have a width of, for example, 2.54 cm (1.0 in). The final width of the flap brush 10 can be chosen with respect to the particular desired application of the flap brush.
When fabricating conventional flap brush 10, it has been observed that it is not always possible to maintain the core 12 concentric relative to the bore of the adhesive coater for all or a portion of the length. Even when the valve inner wall 62 is sized to guide the core 12, it is not possible to always maintain desired concentricity. This can be caused, for example, by tolerances between the core outer surface and the valve inner wall 62 and by tolerances between the valve 60 and the bore 52. These tolerances can allow the core to be non-concentric relative to the bore, and this can be aggravated by the distance between the bottom of valve 60 and the top of the bore 52 when the valve is moved to its open position. Additionally, the core 12 may exhibit excessive out-of-roundness along all or a portion of the length of the core. Either or both of these conditions can cause a portion of the outer surface 14 of the core to come too close to or contact the wall of the bore of the adhesive coater as illustrated at C in FIG. 3. Under these conditions, the adhesive layer 16 may not have uniform thickness around the circumference of the core or along the length of the core, or both. When the adhesive layer 16 is not uniformly distributed over the outer surface 14 of core 12, those flap brushes 18a that contact little or no adhesive coating on the core are not adequately adhered to the core, and may leave a gap 26 between outer surface 14 and core end 20 of flaps 18a as seen in FIG. 4. The compressive force between adjacent abrasive flaps 18 and 18a may be insufficient to maintain unadhered abrasive flaps 18a on the flap brush 10, thereby reducing the effectiveness and life of the flap brush.
It is therefore desirable to provide an abrasive flap brush with a core having a sufficiently uniform coating of adhesive and a method and apparatus for making an abrasive flap brush having a uniform layer of adhesive disposed on the core to ensure adequate adhesion of the abrasive flaps to the core.